Mechanism and controls for controllable aircraft propellers



H. M. M COY June 26, 1945.

MECHANISM AND CONTROLS FOR CONTROLLABLE AIRCRAFT PROPELLERS Filed Nov.18, 1942 6 Sheets-Sheet l //v we 70/? Q0 /7. C60,

Jrroeazey June 26, 1945. H. M. MCCOY MECHANISM AND CONTROLS FORCONTROLLABLE AIRCRAFT PROPELLERS Filed Nov. 18, 1942 6 Sheets-Sheet 2koe r TORNE V June 26, 1945. McCOY 2,378,938

MECHANISM AND CONTROLS FOR CONTROLLABLE AIRCRAFT PROPELLERS Filed Nov.18, 1942 6 Sheets-Sheet 3 Hon 44 0 MM Cor TTO/PNF we June 26, 1945.

H. M. MCCOY 2,378,938

MECHANISM AND CONTROLS FOR CONTROLLABLE AIRCRAFT PROPELLERS Filed Nov.18, 1942 6 sheets -sheet 4 Cor H. M. M COY June 26, 1945.

MECHANISM AND CONTROLS FOR CONTROLLABLE AIRCRAFT PROPELLERS Filed Nov.18, 1942 6 Sheets-Sheet 5 u 2 w i 4 00 u 46 was 2 22 2 b 8 2 2 2 3 8 2 2n m u Tufl nfl h v V7 k m m s W L.. 7 .1 m 2 0 8 l2 2 a w w m a z M 02 am 0 E m 8 8 T m n M. n 2 7 June 26, 1945. cco 2,378,938

MECHANISM AND CONTROLS FOR CONTROLLABLE AIRCRAFT PROPELLERS Filed Nov.18, 1942 6 Sheets-Sheet 6 Han 42o M COO Patented June 26, 1945 UNITEDSTATES PATENT OFFICE MECHANISM AND CONTROLS FOR CON- TROLLABLE AIRCRAFTPROPELLERS (Granted under the act of March 3, 1883, as amended April 30,1928; 370 0. G. 157) 22 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to variable pitch propellers for aircraft, andparticularly to mechanism whereby the pitch of the blades may becontrolled either automatically or manually over a wide range, extendingin one direction in the positive pitch range for full feathering and inthe other direction in the negative pitch range for propeller braking.

Neither the idea of full feathering the propeller of a defective enginein a multiengined craft to minimize its drag and to stop a damagedengine, nor the idea of adjusting the propeller to a negative pitchangle for braking, is broadly new; yet, up to the present, no whollysatisfactory mecha-- nism has been proposed which would operate tochange the pitch rapidly enough for attaining the feathering and brakingpositions in a matter of one or two seconds, and still operate slowlyand accurately enough to accomplish the microadjustments required tomaintain a preselected propeller speed within one or two R. P. M., as isparticularly required in multiengined craft.

Employment of gear mechanism whereby pitch change is accomplished byapplying one or the other of a pair of brakes to rotate the propellerblades in one or the other direction for pitch increase or decrease is awell-known expedient. yet it is one of the most satisfactory ways knownfor effecting large pitch changes in minimum time, inasmuch as theconsiderable power required for these rapid pitch changes is derivedfrom the source of propeller rotation, that is, from the ensine of thecraft, so that the matter of whether the engine loses slightly in R. P,M. due to the considerably increased load of rapid pitch change is of nogreat moment at the time these changes are being effected.

On the other hand, the micro-adjustments in blade pitch, necessary tocorrect off-speed conditions of one or two R. P. M., may be as small asone one-hundredth degree, and these had preferably be made withoutcalling directly on the engine to supply the power for effecting thecorrection of its own speed, as, for instance, by means of a smallelectric or hydraulic motor with an unusually large gear reductionbetween the motor and propeller blade. the reduction preferably beingsomewhere between ten thousand and fifteen thousand to one. Thismotor-operated blade-adjusting mechanism has the further advantage that,unlike the braking system of blade adjustment. it will operate when theengine is stopped, whereby the blade pitch may be brought back to thetake-oil pitch angle from the negative braking pitch angle if that wasnot done, upon alighting, before the engine came to a full stop, orunfeathering may be accomplished on an engine stopped by feathering thepropeller.

It is. therefore, an object of this invention to so connect andcoordinate the two above-discussed systems of pitch adjustment that eachmay operate to do the adjusting for which it is best fitted, withoutdisconnecting or otherwise aflecting the other.

Other objects will be apparent from the following specificationconsidered with respect to the drawings, wherein,

Figure 1 is a schematic illustration of the device in its simplest form.

Figures 2, 3 and 4 are schematic illustrations of variants of the deviceshown in Figure 1.

Figure 5 is an axial section through a variable pitch propeller whichembodies the principles of the invention.

Figures 6 through 10 show, in somewhat greater detail, a variant of thedevice shown in Figure 5.

Figure 11 shows a governing and control mechnism such as shouldpreferably be provided for operating the device shown in Figures 6through 10.

Like numerals refer to like parts throughout the drawings.

Referring to Figure l, a propeller shaft 20 drives a propeller hub 22which houses and provides bearings for the two-stage worm gearing. Aworm 24, rotatable on a shaft 26. between bearing hubs 28, meshes withworm wheel 30 which is attached to the shank of the blade 32. A shaft34, rotatable in bearings 36, at the rear end carries an elongated gear38 and at the front end a worm 4B. A worm wheel 42 is fast on the end ofthe shaft 26 and is in mesh with the worm 40.

The elongated gear 38 meshes with a narrower faced gear 44 which isfreely rotatable on the shaft 20. A second elongated gear 46 rotatesfreely on a stud 48 supported in a boss 50 in the hub 22, the secondelongated gear being meshed with the narrower gear 52. The faces of theelongated gears 38 and 46 overlap and mesh with each other at 54,whereby, if either of the narrower gears 44 or 52 rotates relative tothe hub 22, the other narrower gear will rotate oppositely. Likewise, ifgear 44 is held against rotation while the hub 22 is rotating, the wormin will be rotated on its own axis in the same direction as the hub, butif gear 52 is held against rotation while the hub 22 is rotating, theworm in will be rotated on its own axis in a direction opposite to thatof the hub. Whether the pitch of the blade 32 is increased or decreaseddepends therefore on which or the two gears 44 or 52 is held orretarded. As long, however, as neither the gear 44 nor the gear 52 isheld against rotation or retarded, the entire gear mechanism willrevolve as a unit without changing the pitch of the propeller blades.The double reduction worm gearing 30, 2|, 42, ll, the elongated pinionsll, 08, and the gears ll, 52, will hereinafter be called thepitch-change gear-set, the worm wheel II being the driven gear. thegears ll, l2, which control pitch change, will be called the ontrolgears, and the other gears of the gear-set, the intermediate gears.

The means for retarding the control gears It and 62 includes a casing itsecured, against rotation, to a nonrotating part II of the engine.Rotatably supp rted in the casing are shafts it and 82, carrying gears64 and 38 respectively. Gear il meshes with a gear I which is joined forunitary rotation with the gear 62 by a sleeve ll, whereas gear 66 mesheswith a gear 10 which is joined for unitary rotation with the gear 44 bya sleeve II, whereby arresting or retarding the shafts Bil or 82, one ata time, will arrest or retard the control gears 52 or N, and therebyrespectively decrease or increase the pitch of the blade 22, assumingthe worm 24 to be right-hand, the worm Ill left-hand, and rotation ofthe hub 22411 the direction of the arrow 12, and assuming that the ratioor the two gears "-48 is l to l, the worm wheel and worm 42-4! is 10 tol, and the worm wheel and worm 20-" is 14 to l, the overall pitch changeratio will be 140 to 1. In order to facilitate description of theoperation of the device of Figure 1, the gears 38, ll, l6, I2, 84, 8.,DI, and ID are herein all made the some in pitch diameter so that a l to1 ratio exists between them. In actual practice these diameters may bevaried to modify the overall ratios to any desired degree within reason.

A hydraulic braking means for arresting or retarding the shafts or 62comprises a pair of pumps II and I6 which are drivably connected to theshafts ill and 82 respectively. Obviously, any restraining force whichretards rotation of either pump ll or 15 will retard rotation either ofthe control gear 52 or H to respectively decrease or increase the pitchoi the blades 22.

, The two pumps II and It, the hydraulic circuits through which theypump, and the valve mechanism which controls the circuits are shownschematically only. The main control valve I8 comprises a valve casingll bored to slidably receive the valve plunger 82, which is made up of arod 84, a long piston 88, and two short pistons 88, the pump dischargeports being connected by conduits 8B and 82, and the pump suction portsby conduits 9| and 98, to the valve casing within the space between thelong and short pistons 86 and 88, whereby when the plunger is positionedcentrally in the casing as shown, fluid circulates freely from the pumpIt through the conduit 90 along the stem 84 and back to the pump throughconduit 84 and at the same time circulates freely from the pump I8through conduit 92 along stem N and back through conduit 88.

As long as fluid may be circulated freely by the pumps 14 and 16,through their external circuits 8II84 and 92-46, no change in propellerpitch will take place. When, however, the valve plunger 82 moveslongitudinally in the casing Bil, one or the other of the pump dischargeconduits will be restricted or closed, depending on the amount ofmovement, whereupon propeller pitch adjustment will take place. If, forinstance, the plunger 82 is moved up to close the discharge conduit ill,the pump ll will practically cease rotating, whereby the shaft 80,pinion Bl and gear 68 must also practically cease rotating, whereupongear 48 rolls around the outer surface of the control gear 52 turningthe gear 54, the shaft II and the worm I in the opposite direction tothat which the propeller hub 22 is rotating; thus operating theleft-hand worm and wheel Ill-42 and the righthand worm and wheel 2llllto decrease the propeller pitch. Obviously, shifting the plunger 82 inthe opposite direction will cause an increase in the propeller pitch.Any convenient means may be used for bringing the plunger 82 within theoperator's reach for manual operation; electric solenoid or other remotemeans may be used or, it may be automatically controlled by centrifugalor like governing means Small conduits 98 return any fluid which mayleak past the pistons l8, to the suction conduits 94 and 96, thence tothe suction sides of the pumps.

In order to avoid severe shock by too sudden a closing of the externalcircuit of one or the other of the pumps, the bypasses 98 and pressurerelief valves IIIII are provided. Valves m may preferably be springloaded and adjusted to yield at a pressure somewhat in excess of thatrequired to hold one of the gears 68 or 10 against rotation when turningthe worm gearing for pitch increase or decrease.

The structure thus far described is included in my copending applicationSerial No. 458,587, filed September 16, 1942, the braking mechanismbeing shown in Figure 2, and the pitch change gearing in Figure 6 ofthat application. These mechanisms do not form a part of this inventionexcept as used in combination with other features hereinafter described.

A differential gear-set I02 Figure 1, subject application, is containedin a, cage Ill! and includes a pair of bevel gears I08 and I08 which aredriven by flexible shaft extension H0 and H2, these extensions beingcontinuations of or additions to, the shafts 60 and 62. Any suitableshafting or gear arrangement may be used in lieu or flexible shafts.Bevel idler pinion H4, rotatable on studs H5, are in constant mesh withgears I98 and I08. A relatively large gear H8 is affixed to the cage Iby screws I 20. The cage I04 itself is the differential pinion carrierfor the gearset. A differential gear-set in some form is required as apart of each of the several modifications of the invention hereinafterdescribed.

The power unit for rotating the carrier IM consists of a small electricmotor I 22 which is arranged to drive the gear IIII through aspeed-reducing gear box I24 and a pinion I26. The gearset in the box I24may preferably have a ratio of about to l, and the ratio between thegear and pinion IIB-l28 may preferably be about /2 to 1. The box I24should also contain a spring-engaged brake for holding the pinion I26nonrotative when no pitch change is desired, and an electricallyengaged, spring-disengaged clutch for connecting the motor I22 andpinion I26 only when electric current is applied to operate the motor. Across section of a small motor with an inbuilt gear box and thenecessary clutch and brake mechanism is shown in Figure 9 and ishereinafter described. A wiring diagram showing the necessaryconnections to the motor and to the electrically operated clutch andbrake mechanism, together with a series of manually and automaticallyoperated switches for controlling the applied current is shown in Figure11. The structure and operation of the mechanism of Figures 9 and 11will be hereinafter discussed in detail. The operation of the mechanismshown in Figure 1 is as follows:

Let us suppose, for illustration, that the operator desires to shiftfrom the take-oil pitch to full feathering, which may represent a pitchchange of approximately seventy-five degrees. He will move the plunger82 in the proper direction to close the discharge conduit 32 of the pumpII. This will cause the pinion and gears "-44 to substantially ceaserotation, whereupon the wide gear 28 will roll around the control gear44, rotating the shaft 34 in the same direction and at the same speed asthe propeller. Assuming a propeller speed of 1120 R. P. M., the 140 to 1worm reduction will change the pitch angle at a rate of 94 8 R. P. M. orat the rate of 8x360 degrees=2880 degrees per minute=48 degrees persecond. The shift to full feathering will therefore be accomplished insomewhat under two seconds.

In shifting from the cruising range to a negative pitch angle forpropeller braking, movement of the plunger 82 upward to close thedischarge conduit 00 of the pump I4 will effect this change inapproximately the same time as for full featherlng, that is, somewhatless than two seconds.

The foregoing use of the pumps I4'I6 takes care of the grosser pitchchange increments 'or decrements which are required to take place inminimum time when full featherin or braking is being effected. The pumps14-10 are, however, operative in this capacity only while the propelleris rotating, and conditions may arise when large pitch changes mayadvantageously be made by use of the motor I22. As an example of such aninstance, assume that the propeller has been left in the brakingposition and the engine stopped, and it is desired to use the electricmotor I22 to obtain the proper pitch angle for takeoff. To accomplishthis change, the blade 32 may be rotated clockwise, that is, in thedirection of the arrow I28; a matter of about 40 degrees.

The shaft 34 must therefore be rotated in the direction of the arrow I2a matter of about xl40=15.55 turns. Since the gears 33, 44, 40, 52, 04,88, I0, 86, are all of the same size and all in mesh one with the next,it is readily found by tracing the directions and degree of rotationthat these gears take, when the shaft 34 is rotated the required 15.55turns, that the bevel gears I06 and I00 must also both rotate 15.55turns and that the direction of both is anticlockwise, viewed from theend of cage I04 to which gear H8 is attached. With a ratio of 140 to 1in the gear box I24, and a ratio of 1 to 1 between the gear H0 andpinion I20, the 15.55 turns of the cage I04 will be accomplished byabout 3266 clockwise turns of the motor. By employing a motor having anormal speed of 7350 R, P. M. the relatively large pitch change of 40degrees is accomplished by means of the motor I22 in 9 35 minutes orabout 2'7 seconds. Stated in another way, themotor I22 is rotated 3266turns clockwise, which, through the 2l0-to-1 reduction provided by thegear box I24 and the pinion I26, causes the gear I I 8, cage I04 andbevel gears I06 and III! to rotate =15.55 turns anticlockwise, allviewed from that end of the motor I22 which is opposite the end fromwhich the motor shaft emerges. This causes gear 04 to rotateanticlockwise and gear 6| clockwise 15.55 turns viewed from the cageI04. Viewed also from the cage I04, the gears 08. 52 and 20 must rotateclockwise and the gears 10, 44 and 48 anticlockwise 15.55 turns. The15.55 clockwise turns of the shaft 34, operating through the l40-to-1worm gear reduction, will rotate the blade "-"mo or turn which amountsto 40 degrees of pitch increase.

The micro-adjustments which are required to accurately maintain aconstant propeller speed while cruising are also accomplished by the useof the electric motor I22. while the pumps are running idle. Forillustration, let it be assumed that the propeller has an on-speedrotation of 1120 R. P. M., and that it has gone overspeed to an extentwhich requires an increase in the pitch angle of 2 degrees, and that itis desired to make this change in the pitch angle at a rate of 1 degreesper second, which requires a total time of 1 /7 seconds. If the normalpropeller rctation speed is 1120 R. P. M., then there will be 32 turnsin 1 /1 seconds.

Since the gear ratio between the shaft 24 and blade 32 is to l, a changeof 2 degrees in the pitch angle of the blade 22 in the direction of thearrow I28 will require a rotation of 140 2*/1=360 rotation or one turnof the shaft 34 clockwise with respect to the hub 22, clockwise being inthe direction indicated by the arrow I2. This one turn of the shaft 24and gear 38, clockwise with respect to the hub 22, rotates the gears 44and I0 one turn anticlockwise with respect to the hub 22, but since thehub 22 has, in the same period of time, rotated 32 turns clockwise withrespect to the stationary housing 00, the gears 44 and 10 will haverotated only 31 turns clocggvise with respect to the stationary housingSo also this one turn of the shaft 24 and gear 30, clockwise withrespect to the hub 22, rotates the idler 48 one turn anticlockwise andthe gears 52 and 00 one turn clockwise with respect to the hub 22, butsince the hub 22 has, in the same period of time, rotated 32 turnsclockwise with respect to the stationary housing 50, the gears 52 and 68will have rotated 33 turns clockwise with respect to the stationaryhousing 00. The gears 64 and 06 will therefore have rotated 33 and 31turns respectively, both anticlockwise with respect to the stationaryhousing 50, while the shaft 34 rotates one turn clockwise on its ownaxis and is bodily revolved about the axis of the hub 22 clockwise 32turns. Bevel gear I will therefore rotate clockwise 31 turns and beveledgear I06 anticlockwise 33 turns, both viewed from the end of the cageI04 to which the gear III is attached. This can be accomplished only ifthe cage I04 rotates through one turn anticlockwise in the same periodof time.

The ratio between the motor I22 and the carrier I04 being 210 to 1, themotor must revolve two hundred ten revolutions clockwise. Since itsnormal speed is 7350 R. P. M. it will revolve the two hundred tenrevolutions in /'rasn ii0=l.'l seconds. An increase of 2/-: degrees in1.7 seconds is equal to an increase of approximately 1 degrees persecond. Decrease of the pitch angle at the same rate may be accomplishedby rotating the motor anticlockwise.

In the schematic view Figure l, the flexible shafts H0 and H2 areemployed for the reason that, with such an arrangement, the two scars 88and 88 which rotate at the same speed and in the same direction, as longas the control gears 88 and 82 both rotate in unison with the propellet,will drive the two bevel gears I88 and I88, to which they are attached,at the same speed but in opposite directions. The flexible shafts andthe manner in which they are attached constitute a reversing means whichis present in one form or another in all of the modificationshereinafter described. These reversing means must in some mannerfunction to take power oil the control gears while they rotate in thesame direction as the propeller hub and transmit it to the twodiilerential gears so as to rotate one of them in a direction oppositethe other. The two of flexible shafts may, for example, be avoided by anarrangement as shown in Figure 2, where the flexible shafts H8 and H2are replaced by 'gid shafts I88 and I32, and a pair of gears I84 and I88are added, gear I88 being drivably connected to the shaft I38, and gearI88 to the hub of the gear I88. Gear I88 is runningly fltted tothe'shaft I32, while gear I88 is drivably secured thereto. The twobrakes I88 and I88 are band brakes instead of hydraulics as in Figure 1,but the hydraulic brakes may be used if desired. In Figure 2, the gearsI34--I88 constitute the reversing means. Other parts of the structureare the same as in Figure l. The arrows of rotation show that the sameresults are accomplished.

Figure 3 shows another arrangement for accomplishing substantially thesame result as that of Figure 1 but with the flexible shaft of Figure 1omitted. In this variant, reversal oi the bevel gear I88 is effected bytaking directly oil the propeller shaft 28 with a pair of gears I82 andI, and an idler gear I88 between, to provide the right direction ofrotation, these gears and pinion constituting the reversing gear-set forthis modification. The bevel gear I88 is drivably secured to the shaftI82, while the bevel gear I88 has its hub freely rotatable on the shaftI82 but drivably secured to the gear I. Brakes I48 and I88 are hereshown as friction brakes consisting of bands I82 which may be drawn upby hydraulic cylinders I88 which are in turn controlled by solenoidoperated valves I88. This device is only half as sensitive formicro-adjustments as those shown in Figures 1 and 2 because, when takingthe drive for one of the bevel diflerential gears on the propellershaft, each turn 01' the carrier I88 eflects twice the change in bladeangle as in the arrangements of Figures 1 and 2. This may,

however, be compensated for by providing a 3 to 1 ratio between thepinion I21 and gear I I8 instead of the 1 /2 to 1 ratio oi! the pinionI28 and gear I I8 of Figure 1.

In the modification Figure 4, the gear 18 which is on the sleeve II inFigure 1, and is used to ar rest or retard the control gear M of Figurel, is eliminated, and a brake I48 put in its place on the sleeve II. Thegear 84 then drives the shaft I88 through which the bevel gear I88 isdriven, the other bevel gear I88 having a long hub to which the gear Iis attached. Gear 88 is driven through the idler pinion I48 by the gear88 which is fast on the control gear 82. A second brake I88 is fast onthe shaft I88. The remainder of the construction and, operation are thesame as described relative to Figure 3.

In Figure a somewhat different type 0: gearing is employed to carry outthe principle of the invention. A miter driving gear I88, a sun gear I88and a shaft I82 are secured together to rotate as one. A planet pinioncarrier I88 comprises a hub I88 which has rotative bearing on the rootof a propeller blade I88, a flange I18 at the lower end of the hub andstuds I12 depending from the flange. The shaft I82 is concentricallysupported for rotation in the hub I88. A series of planet pinions I18are rotatable on the studs I12 and are thereby held in constant meshwith the sun gear I88.

An inwardly flanged internal ring gear I18 is secured to an outwardlyextending flange on the blade I88 by pins I18 whereby the blade I88 andgear I18 rotate as one on the bearings I18, the gear I18 being thedriven gear of the gear-set. A second internal ring gear I88 isnonrotatably secured in the propeller hub I82 by screws I88, the gearI88 bein the reaction gear of the planetary gear-set. The planet pinlonsI14 have a lace width as wide as the two internal gears I18 and I88together, and have a peripheral groove I88 dividing their face into twoparts. The sun gear I88 has a face width which engages only the lowerone oi these parts.

If the sun gear is provided with twelve teeth. the planets with twelveteeth each, and the lower ring gear I88 with thirty-six teeth, thecarrier rotations will be S hi? l Rfi-36+12-4 the sun gear rotations Ifthe upper ring gear I18 is provided with thirtyfive teeth, the bladerotation will be ;g the sun gear rotations but in the oppositedirection. I! four pinions I18 are equally spaced around the carrierflange I18, only the first will have the teeth of the upper and lowerhalf in alignment. The second, third, and fourth will respectively havethe teeth of the upper half in advance of the lower half /4, [2, and oi.the circular pitch. In designing for other ratios than that abovesuggested, it should be noted that the lower ring gear I88 and the sungear I88 should,

both have a number of teeth which is divisible by the number of equallyspaced planets on the carrier, or the number of-teeth on both may bedivisible by half the number of pinions on the carrier if neither isdivisible by the whole number of pinions on the carrier.

In mesh with the miter driving gear I 58 are two miter control gears I88and I88, the first being on the long sleeve it? which is freel rotatableon the propeller shaft 28, and the second on a shorter sleeve I88whichis freely rotatable on the long sleeve I82. The short sleeve I88carries the brake drum I88, the longer sleeve I82 being provided with asimilar brake drum I88. Friction bands 288 and 282 are arranged to beapplied to the drums I88 and I88 by fluid pressure means 288 and 288,which are mounted on the stationary housing 288. The assembly of thespur gears I18, I88 and I68, spur pinions I14 and carrier I88, and themiter gears I88, I88, and I88, constitute the pitch-change gear-set ofwhich the ring gear I18 is the driven gear and the miter gears I88 andI88 are the control gears. A reversing gear-set which takes the place ofthe flexible shafts H8 and H2 of Figure 1, comprises a bevel gear 2I8fast on the shaft 28, a bevel gear 2I2 rotatable on a short shaft 2 inthe housing 288 and a bevel gear 2 I 8 rotatable freely on the longsleeve I82, the three bevel gears being in mesh one with the other.

A diil'erential gear-set comprises a, bevel gear 2I8 fast on the longsleeve I 82, a bevel gear 228 pinned to the reversing gear 2I8 forunitary rotation therewith, and bevel pinions 222 rotatable on studs224. Studs 224 are circumferentially spaced apart in a pinion carrier228 which is freely rotatable on the long sleeve I92. A difi'erentialdrive gear 228 is fast on the outside of the carrier 228. A motor pinion238 is in constant mesh with the gear 228. The ratio of the pinion 288to the gear 228 is preferably about 3 to l.

The electric power unit 232 should have an inbuilt clutch and brakemechanism and a speedreducing gear set similar to that called for in thediscussion of Figur 1, The arrow 12 on the front end of the propellerhub indicates the preferred direction of rotation. The operation of thedevice shown in Figure 5 is as follows:

Let us assume, for illustration, a propeller R. P. M. of 1120 in thedirection of the arrow 12. If the brake drum I98 is now held againstrotation, the miter gear I90 stops and the miter gear I58 rolls aroundit, thereby rotating on its shaft I82 in a direction opposite to that ofthe arrow 234 and at the same R. P. M. as the propeller. Since the ratiobetween the gear I88 and the blade I88 is 140 to l, the blade will beturned on its axis 8 R. P. M.=2880 degrees per minute or 48 degrees persecond in the direction of the arrow 234, which is the direction forincreasing the pitch. Arresting rotation of the brake drum I98 decreasesthe pitch at the same rate.

Changing the blade angle when the propeller is not rotating isaccomplished by the motor 282. In this case the propeller hub I82, shaft28, bevel gears 2I0, 2I2, 2I8, and 220, are nonrotative. When thecarrier 228 is now rotated by means of the motor in the direction of thearrow I2, the bevel pinions 222 will roll around the nonrotative bevelgear 228 and will rotate the bevel gear 2I8, 1

sleeve I92, and miter gears I88 and I58 at twice the speed of thecarrier 228. If the motor has an inbuilt reduction gear-set of 140 to 1,the motor pinion 238 to the carrier gear 228 a ratio of 3 to 1, and thepitch-change gear-set a ratio of 140 to l, the motor armature willrotate 29,400 turns to i of the blade. Forty degrees or /9 of a bladerotation would require 3266 motor revolutions. A motor having a normalspeed of 7350 would therefore require about 27 seconds to move thepropeller blade through forty degrees change in pitch angle when thepropeller was nonrotative.

As to making the micro-adjustments necessary for uniform propellerrotation, let us assume, for illustration, that the propeller has goneoff its normal speed to an extent which will require an increase in thepitch angle of 2% degrees, and that it is desired to make this change inthe pitch angle at a rate of 1% degrees per second or in a total time of1 seconds.

Since the gear ratio between the sleeve I92 and the blade I88 is 140 to1, a chang of 2% degrees in the pitch angle of the blade I88 in thedirection of the arrow 234 will require a rotation of 140 2i=6=360degrees, or one complete turn, which the sleeve I92 must gain on the hubI82 to effect this change.

If normal propeller rotation is 1120 R. P. M., then there will be 32turns in 1 seconds. The shaft 20, gears 2Ill, 2I2, 2l8, and 220,therefore make 32 turns. To effect that pitch change the gear 2I8therefore must rotate 33 turns in the direction of the arrow 12, whilethe gear 220 rotates 32 turns oppositely. Since it is a condition of anon-rotating carrier 228 that gears H8 and 220 rotate oppositely at thesame speed, it will be seen that when the gear 2I8 rotates an additionalturn, the carrier 228 must rotate one-half of a turn in the direction ofthe arrow 12.

Since this half-turn is to be accomplished in 1% seconds, the carriermust rotate at the rate of 17 R. P. M., the pinion 288 must rotate 3 l7=52 R. P. M. and the motor armature will rotate l40 52/ =735U R. P. M.To efiect the desired pitch increase, the motor armature rotates at thisspeed for 1 seconds, in which time it must make two hundred turns. Ifthe same type searing is used in the motor gear-set as in the bladeSear-set, the motor will'rotate clockwise to increase the propellerpitch. Anticlockwise rotation of the motor will decrease the pitch atthe same rate.

Figures 6 through 11 show a specific exemplification of the inventiontogether with the electric motor structure and its manual and automaticcontrols.

Referring to Figure 6, the propeller hub I82, blade I88, gears I18, I88,and I80, pinions I14 and their pinion carrier I84, and the miter gearsI58, I88, and I98, are, both as to construction and operation, exactlylike corresponding parts of the structure of Figure 5 heretoforedescribed and reierred to as the pitch-change gear-set, the miter gearsI88 and IIIII being, as before, the control gears. The reversinggear-set and the diflerential gear-set, however, both differ from thestructure of Figure 5 in several material respects In Figure 8, themiter control gear I88 is fast on a long sleeve 288 which is freelyrotatable on the shaft 28. Sleeve 238 extends rearwai'diy into thenonrotatable housing 238, and at the rear end has fast thereon a brakedrum 248.

The other miter control gear I90 has a hub upon the rear end of winchare formed the teeth of a. spur gear 242. A second brake drum 244 isaxially spaced apart from the brake drum 240 within the housing 288.Drum 244 has a hub upon the forward end of which are formed the teeth ofa spur gear 248 which may preferably, although not necessarily, be ofthe same diameter as the gear 242.

The forward wall 248 of the housing 238 is thicker than the other walls,occupying th entire space between the gears 242 and 248 and providing,at its central part, a bearing for the long sleeve 238. Fans ofcup-shaped openings (see Figure 10) are formed in opposite sides of thewall 248, but do not extend all the way through it, thereby leaving athin portion 250 in which the studs 282 have their ends anchored.Reversing plnions 254 are freely rotatable on the studs 252, the studsbeing so spaced and positioned that the inner ends of the pinionsoverlap and are in mesh one with the other, and the outer ends 288 and258 which extend oppositely from the wall 248 are in mesh with the gears242 and 248 respectively (see Figure 6), whereby rotation of the gear242 in one direction rotates the gear 248 in the opposite direction.Gears 242 and 248 and pinlons 254 may collectively be referred to as thereversing gear-set which, in some form or other is present in all of themodifications herein shown. As long as there is no pitch change takingplace, the miter control gears I88 and I90 both rotate at the same speedand both in the direction of the arrow 12, whereby the brake drum 248rotates in the direction of the arrow" but due to the reversing gear-setthe brake drum 244 rotates in the opposite direction.

The space between the brake drums 248 and 244 is occupied by a.relatively thick disc 280 which also has pockets fanned in oppositesides of the disc and pairs of pinions 232 rotatable on studs 284anchored in the bottoms of the pockets in the samemanner as wasdescribed relative to Figure 10, where the inner ends of the pinionsoverlap and mesh one with the other and the outer ends extend beyond thedisc.

252, however, mesh with a pair of internal gears 288 and 288 which areformed on the inside of the drums 244 and 243 respectively. Inasmuch asthe reversing pinions 254-288 cause drums 248 and 244 to rotateoppositely at the same speed, as long as no pitch change is beingeffected, the pinions 232, by meshing with the oppositely rotatinginternal gears 288-288, will cause the disc 288 to remain nonrotative aslong as the no-pitch-change condition prevails. The internal gears268-283, the pinions 282, and the disc 238 comprise a spur differentialgearset which functions exactly like the bevel differential gear-sets inFigures 1 through 5, the parts 6-463-282-2813 of this spur differentialcorresponding respectively to parts 8-183- 114-184 of the beveldifferential shown in these views, and while it is indicated that thepitch-changin gear-sets which are to be used in Figures 2, 3, and 4 are,like Figure 1, of the worm-gear type. and those used in Figures 5 and 6are of the planetary type, it will of course be understood that theprinciples of the invention will be carried out if the worm pitch-changegears of Figure l are used with the differential gearing of Figure 5 or6 and if the planetary pitch-change gearing of Figure 5 or 6 arecombined with the diflerential gearing of Figures 1 through 4. InFigures 1 through 4, the control gears are 44 and 52, while in Figures 5and 6, the control gears are 188 and 133. To adapt Figures 2, 3, and 4to receive the planetary pitchchange gear-set, the spur control gears44-52 should be exchanged for the bevel control gears 183-488.

. Brake bands 213 and 212 are arranged to be applied with solenoids 214and 218 to respectively arrest or retard the drums 244 and 243. A bevelgear 213 is formed on the periphery of the disc 288, this gear being inmesh with the bevel pinion 284 of the motor 282. The speed ratio betweenthe pinion and gear 280-218 may preferably be 3 to 1. The motor may besecured to the housing 233 by any convenient means. The construction ofthe motor is shown in Figure 9.

The motor housing 234 has hearings in the end walls for the low-speedmotor shaft 288 to the forward end of which the bevel pinion 288 issecured. The motor housing 284 is divided by partitions 285 and 281 intothree compartments: :1 motor compartment 288, a clutch and brakecompartment 288, and a gear compartment 222.

The armature 284 is built on a sleeve 238 which is freely rotatable onthe shaft 283 and at its forward end carries the clutch disc 238. Tosimplify reversing of the motor, two sets of oppositely wound fieldcoils 388 and 382 are used, although the conventional method ofreversing the direction of the armature current as is the more commonpractice may be followed.

A clutch-and-brake disc 384 faced with friction material 338 is heldagainst the partition wall 281 by the expansion spring 383. A coil 388is fixed in the compartment 233 and adapted, upon energization, to drawthe disc 884 away from the wall 281 and against the clutch disc 288. Thehub of the disc 334 extends through the wall 233 through a jaw ins teethof asvacss 281 into the gear compartment 292, the teeth of a sun gear318 being formed on the forward end of the hub.

A planet pinion carrier 312 is freely rotatable on the hub of the disc304 and carries the studs 314 upon which the planet pinions 313 rotatefreely, the pinions being in constant mesh with the sun gear 318. A ringgear 818 is held against rotation in the compartment 232 by the screws328. Ring gear 318 is in constant mesh with the planet pinions 316. Asecond ring gear 322, which is also in constant mesh with the planetpinions 318, is drivably connected to the shaft clutch 324, theintermeshing teeth of which are formed on the rear end of the hub of thegear 322 and the forward end of an enlargement of the shaft 288. Theintermeshthe clutch 324 are held in engagement by a spring 326. A coil328 held in the end of the compartment 232, when electrically energized,draws the gear 322 forwardly against the resistance of the spring 326whereby the teeth of the clutch 324 are disengaged and the shaft 286 maybe turned freely by the pinion 283 without turning any other part of themotor.

The planet pinions 318 each have their relatively wide faces dividedinto two parts by a groove 338, the sun gear 3111 and the ring gear 318being meshed with one of these parts while the ring gear 322 only ismeshed with the other of said parts. The sun gear 313 has twelve teeth.the planet pinions 318 each have twelve teeth, the ring gear 318 hasthirty-six teeth and the ring gear 322 has thirty-four teeth whichprovides a ratio through the motor gear-set of 68 to 1. It should benoted that if, in this gear-set, only two planet pinions are used, theteeth on the two portions of the pinion will be in alignment but if fourare used, two of them will have so the teeth on one part half thecircular pitch out of alignment with the teeth on the other part. Indesigning for other ratios it may be useful to remember that if thenumber of teeth by which the stationary ring gear 318 differs from therotatable ring gear 322 is the same as the number of planet pinions 316,and the teeth of both the sun gear 313 and ring gears 318-322 aredivisible by the number of planet pinions, or by half the number ofplanet pinions if the teeth of neither the sun or ring gears aredivisible by the whole number of planet pinions, then the planet pinionsmay all be exactly alike and all have the teeth extending uniformlyacross their wide face, in which case the groove 83B is unnecessary andthe sun gear may have as wide a face as the planet pinions or as wide asthe two ring gears taken together.

Since the rotation of the shaft 288 is a function of the pitch change,it is prolonged at the rear end and screw-threaded as at 332 for theinternally threaded carriage 334 which moves along the screw as itrotates in one or the other direction to operate the pitch indicator 333through a "Bowden wire 338 or other similar means. Since the degree ofpitch change is preferably kept within predetermined limits, thecarriage 334 is also employed to operate a series of switches whichfunction to limit the change in pitch angle by breaking the electriccircuits. The electric switches and other control means are shown inFigure 11,

Referring to Figure 11, a centrifugal governor 848, which may be drivenby the engine or propeller shaft through the gearing 342, operates anelectric switch 344, which consists of a stationary contact member 346and two contact members 343 and 356 which are insulatedly spaced on theblock 362, the block being pivoted at 364.

The stem 356 of the governor is attached to the switch at 353, whereby,when an overspeed condition prevails, the contact member 360 engases thecontact member 346 for pitch increase, and when an underspeed conditionprevails, the contact member 343 will engage the contact member 346 forpitch decrease. A spring 363 is adJustable by a rack 362 and pinion 364to vary the R. P. M. at which the switch 344 is actuated to increase ordecrease the pitch.

A manually operable switch 366 has a bar 333 which is constrained by thesprings 316 to remain in contact with the middle contact member 312through which a source 314 supplies current to the automatic contactmember 343. The bar 366 may, however, be manually held in engagementwith the contact members 316 or 313 for energizing the solenoid 214 or216, whereby the brake bands 216 or 212 are applied to efl'ect largeincrements of pitch change as for feathering or braking. Since eitherthe full feathering or the braking position may be accomplished in amatter of about two seconds, no means is provided for preventing thesprings 313 returning the bar 366 to the middle or automatic positionwhen it is released.

The limit switches 336 and 332 are so positioned as to be opened by thecarriage 334 when the automatic switch has respectively increased thecruising pitch to about 55 degrees or decreased it to the take-oil pitchangle, which is about 15 degrees. The limit switches 334 and 366 are sopositioned as to be opened respectively by the carriage 334 at the fullfeathering position, which may be about plus 8'? degrees, and at themaximum braking position, which may be about minus 30 degrees, shouldthe switch bar 368 be held on the contacts 316 or 313 for more than theseveral seconds required to reach these positions.

A snap-action reversing switch 333 is provided and so positioned thatjust before the carriage 334 passes an arbitrary low or negative pitchangle, the switch is operated, whereby the connection between thegovernor contact member 343 and motor winding portion 333 and theconnection between the governor contact member 363 and motor windingportion 332 are reversed, whereby the governor 346 becomes operative tomaintain the selected constant propeller speed in the negative range aswhen braking. Under this reversed condition the movement of the carriage334 to the left, which before represented pitch decrease, now representsnegative pitch increase, and the indicator 336 should hav graduations tocorrespond. A limit switch 336 is provided and 50 positioned as to limitthe negative pitch increase which may be eflected by the automaticgovernor to a matter of about minus 25 degrees. A manually operableswitch 332 may be opened to render the entire electrical systeminoperative.

With electrical conductors connecting the several-parts as shown inFigure 11, the operation of th mechanism shown in Figures 6 through 11will be substantially as follows:

Let us assume, for illustration. that the switch 332 is closed, thepropeller is rotating 1120 R. P. M. in the direction of the arrow 12,and it is desired to full leather. 'The switch bar 363 is held on thecontact member 316 a. matter of several seconds. In this time thesolenoid 214 will have applied the brake band 216, the coil 323 willhave disconnected the gear 322 from the motor shaft 266, thus leavingthe shaft 236 free to rotate and operate the carriage 334 without havingto rotate the motor through the motor gear-set, which, when driven fromthe shaft 236 would otherwise become a high ratio pitch-increasinggear-set, while the miter control gear I66, by remaining nonrotative,will have caused the miter gear I66 to roll around it a matter of aboutsixty-two turns, which will have rotated the propeller blade in thedirection of the arrow 234 a matter of about degrees. In thisfull-feathered position the carriage 334 will open the limit switch 334,the indicator 333 showing the full-feathered position. Ii thisfull-feathered position is to be maintained, the switch 332 may beopened, after which the bar 366 may be released.

Assume now that it is desired to effect propeller braking. The switchbar 363 is held on the contact member 316 a matter of several seconds.The solenoid 216 (see Figure 6) applies the brake band 212, the coil 323trees the shaft 236 from the motor gear-set, while the miter controlgear 166, by remaining nonrotative, causes the miter gear I66 to rollaround it. which will rotate the propeller blade in a direction oppositethe arrow 234, and will rotate the shaft 266 Figure 9 to operate thecarriage 334. Carriage 334 will operate the reversing switch 363 Justbefore the blade passes the arbitrary low or negative pitch angle, thenwill continue to th left until the limit switch 336 opens the circuit.If it is desired to maintain this braking pitch, the switch 332 shouldbe opened before the bar 368 is released. If, however, the switch 332 isleft closed, and the switch bar 363 is released, the automatic governor346 will function to maintain the propeller blades at such pitch angleas will keep the propeller on speed during the entire braking period.Holding the bar 363 on the contact member 316 for one or two secondswill bring the blades back into the positive pitch range, and set thereversing switch to normal.

As long as the switch 366 is left in its normal position, as shown, thegovernor 346 will operate to increase the pitch on overspeed anddecrease the pitch on underspeed by engaging the contact member 343 withmembers 363 and 343 respectively, thereby rotating the motor 262 in oneor the other direction to effect a gain or'loss in revolutions betweenthe internal gears 266-266 and so between the miter control gears133-136 whereby small increments of pitch change put the propeller backon speed.

It will be noted that the coil 363 which engages the clutch forconnecting the motor armature 264 to the motor gear-set is energizedeach time the motor winding is energized whether for one direction ofrotation Or for the other. Since the spring 336 applies the brake 334instantly the switch 344 opens, the motor gear-box inertia efl'ect isvery small.

It should also be noted that the motor brake 334 is always applied tohold the motor gear-set nonrotative when the jaw clutch 324 is eitherbeing engaged or being disengaged, whereby no clashing of the Jaws ofthe clutch 324 ever occurs.

It is further pointed out that while micro-increments of pitch changeare preferably made with the motor 232, it may be advantageous, when thepropeller is nonrotative and the brakes 216-412 therefore not operativefor pitch changing, to makelarger pitch changes with the motor althoughit will require considerably more time.

Attention is directed to the fact that in Figures 1, 2, and 6, the twodifferential gears are drivably connected to the two control gears, oneof the connections including a reversing means, while in Figures 3, 4,and 5, one dlflerential gear only is connected to a control gear and theother to the propeller shaft, one of the connections also being througha reversing means. It will be seen that at least one differential gearmust be connected to a control gear, so that variation in differentialgear speed, above or below propeller speed, will rotate the control gearwith respect to the hub for pitch change. By means of a reversible motortherefor the pitch may be increased or decreased by rotating the samecontrol gear one direction or the other.

While, in all of the several views shown, the braking means is employedfor the grosser pitch changes and the elctric motor is utilized for thesmaller pitch changes, it will of course be understood that retarding ofthe control gears may be omitted in a structure in which only thesmaller adjustments are desired. Such modified structure is broadlydisclosed in my copending application Serial No. 458,039 (see Figure 2or that application), specific examples only of the structure beingincluded herein.

Having described an embodiment of my invention and several variantsthereof, I claim:

1. An adjustable pitch propeller for self-propelled craft comprising ahub, blades having their roots rotatable in said hub about the bladeaxis, pitch-change gear-sets in said hub rotatable as a unit with saidhub, individual gears of said gear sets being rotatable relative to saidhub, said gear-sets each including a driven gear on the blade root, twocontrol gears both coaxial with said hub and both rotatable relativethereto, and intermediate gears between the control gears and the drivengears, adapted, upon relative backward rotation oi one control gear,with respect to the hub rotation, to rotate the driven gears for pitchincrease, and adapted, upon relative backward rotation of the othercontrol gear, with respect to hub rotation to rotate the driven gearsfor pitch decrease, a differential gear-set comprising two dilierentialgears with axes coincident with the hub axis, a differential carriernormally nonrotative' with respect to said craft but rotatable aboutsaid coincident axes for effecting pitch change, diflerential pinionsrotatably carried by said diflerential carrier in mesh with saiddifferential gears, two power transmitting means, each drivablyconnecting one control gear to one differential gear, a reversing gearset having input and output gears both with axes coincident with the hubaxis included in one of said power transmitting means, whereby, uponunitary rotation of both said control gears in the same direction, saiddiflex-ential gears rotate at the same speed in opposite directions whenno pitch change is being eflected, whereby said diiierential carrierremains noniotative with respect to said crart when said control gearsrotate as one with said hub, means to retard said differential gears,one at a time, to produce relative backward rotation of one or the otherof the control gears with respect to said hub rotation. and means torotate;

said diflerential carrier in one or the other direction with respect tosaid craft to provide relative rotation in one or the other directionbetween said control gears and said hub.

2. An adjustable pitch propeller for self-propelled craft comprising ahub, blades having their roots rotatable in said hub about the bladeaxis, pitch-change gear-sets in said hub rotatable as a unit with saidhub, individual gears of said gearsets being rotatable relative to saidhub, said gearsets each including a driven gear on the blade root. twocontrol gears, both coaxial with said hub gara es and both rotatablerelative thereto, and intermediate gears between the control gears andthe driven gears, adapted, upon backward rotation oi one control gearwith respect to the hub rotation, to rotate the driven gear for pitchincrease, and adapted, upon backward rotation of the other control gear,with respect to hub rotation, to rotate the driven gear for pitchdecrease, means to retard said control gears one at a time to producerelative backward rotation of the retarded control gear with respect tosaid hub rotation, a diflerential gear-set comprising two dlfiierentialgears with axes coincident with the hub axis, a diflerential carriernormally nonrotative with respect to said craft but rotatable about saidhub axis for efl'ecting pitch change, differential pinions rotatabiycarried by said differential carrier in mesh with said differentialgears, two power transmitting means, the first power transmitting meansdrivably connecting one control gear to one differential gear forunitary rotation, and the second power transmitting means drivablyconnecting the propeller hub to the other diu'erential gear, a reversinggear set included in said second power transmitting means, having inputand output gears with axes coincident with the hub axis whereby, uponunitary rotation of said control gears and said hub in one direction,said differential gears rotate at the same speed in opposite directionswhen no pitch change is being eir'ected, whereby said difierentiaicarrier remains nonrotative with respect to said craft whenever saidcontrol gears rotate as one with said hub, and means to rotate saiddifierentlal carrier in one or the other direction with respect to saidcraft to provide relative rotation in one or the other direction betweensaid control gears and said hub.

3. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its route rotatable in said hub about the blade axis, apitchchange gear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reaction gear fast in said huband held against rotation with respect thereto, an internally tootheddriven gear within said hub secured to said blade root to be driventherewith, a planet pinion, a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both said ring gears, a sun gear rotatably supported in saidcarrier in mesh with said pinions, a bevel driving gear secured to saidsun gear for unitary rotation therewith, two coaxial bevel control gearsin mesh with the first said bevel gear, adapted upon relative backwardrotation of one control gear with respect to the hub rotation, to rotatethe driven gear for pitch increase, and adapted upon relative backwardrotation of the other control gear with respect to hub rotation, torotate the driven gear for pitch decrease, a difierential gear-setcomprising two differential gears with coincident axes, a differentialcarrier normally nonrotative with respect to said craft but rotatableabout said coincident axes for eiiecting pitch change, differentialpinions rotatably carried by said carrier in mesh with said difierentialgears, power transmitting means operative upon rotation 01 said hub inone direction for rotation said differential gears in oppositedirections when no pitch change in one direction for rotating saiddifferential gears being driven by one of said control gears, wherebysaid carrier remains nonrotative with respect to said craft when saidone control gear rotates as one with said hub, and means to rotate saidcarrier in one or the other direction with respect to said craft toprovide relative rotation in one or the other direction between saidcontrol gears and said hub.

4. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitchchange gear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reaction gear last in said huband held against rotation with respect thereto, an internally tootheddriven gear within said hub secured to said blade root to be driventherewith, a planet pinion, a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both said ring gears, a sum gear rotatably supported in saidcarrier in mesh with said pinions, a bevel driving gear secured to saidsun gear for unitary rotation therewith, two coaxial bevel control gearsin mesh with the first said bevel gear, adapted upon relative backwardrotation of one control gear with respect to the hub rotation, to rotatethe driven gear for pitch increase, and adapted upon relative backwardrotation of the other control gear with respect to hub rotation, torotate the driven gear for pitch decrease, means to retard said controlgears, one at a time to produce relative backward rotation of theretarded control gear with respect to said hub rotation, a diii'erentialfear-set comprising two difl'erential gears with coincident axes, adiii'erential carrier normally nonrotative with respect to said craitbut rotatable about said coincident axes for effecting pitch change,diti'erential pinions rotatably carried by said carrier in mesh withsaid diflerential gears, power transmitting means operative uponrotation of said hub in one direction for rotating said difl'erentialgears in opposite directions when no pitch change is being efl'ected, atleast one of said differential gears being driven by one oi said controlgears, whereby said carrier remains nonrotative with respect to saidcraft when said one control gear rotates as one with said hub, and meansto rotate said carrier in one or the other direction with respect tosaid craft to provide relative rotation in one or the other directionbetween said control gears and said hub.

5. In an adjustable pitch propeller tor a selfpropelled craft. a hub, ablade having its root rotatable in said hub about the blade axis, apitchchange gear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reaction gear fast in said huband held against rotat on with respect thereto, an internally tootheddriven gear within said hub secured to said blade root to be driventherewith, a planet pinion,'a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both said rin gears, a sun gear rotatably supported in saidcarrier in mesh with said pinions. a bevel driving gear secured to saidsun gear for unitary rotation therewith. two coaxial bevel control gearsin mesh with the first said bevel gear. adapted upon relative backwardrotation oi one control gear with respect to the hub rotation. to rotatethe driven ear for pitch increase, and adapted upon relative backwardrotation oi the other control gear with respect to hub rotation, torotate the driven gear for pitch decrease. a differential gear-setcomprising two diil'erential gears with coincident axes, a differentialcarrier normally nonrotative with respect to said craft but rotatableabout said coincident axes for effecting pitch change, differentialpinions rotatably carried by said difl'erential carrier in mesh withsaid diflerentlal gears, two power transmitting means, each connectingone control gear to one differential gear, operative upon rotation ofboth said control gears in the same direction for rotating saiddiiierentlal gears in opposite directions when no pitch change is beingeii'ected, whereby said differential carrier remains nonrotative withrespect to said craft when said control gears rotate as one with saidhub, and means to rotate said diflerential carrier in one or the otherdirection with respect to said craft to provide relative rotation in oneor the other direction between said control gears and said hub.

6. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitchchange gear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reaction gear fast in said huband held against rotation with respect thereto, an internally tootheddriven gear within said hub secured to said blade root to be driventherewith, a planet pinion, a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both said ring gears, a sun gear rotatably supported in saidcarrier in mesh with said pinions, a bevel driving gear secured to saidsun gear for unitary rotation therewith, two coaxial bevel control gearsin mesh with the tlrst said bevel gear, adapted upon relative backwardrotation of one control gear with respect to the hub rotation, to rotatethe driven gear for pitch increase, and adapted upon relative backwardrotation of the other control gear with respect to hub rotation, torotate the driven gear for pitch decrease, means to retard said controlgears, one at a time, to produce relative backward rotation of theretarded control gear with respect to said hub rotation, a difi'erentialgear-set comprising two diii'erential gears with coincident axes, adifferential carrier normally rotative with respect to said craft butrotatable about said coincident axes for eil'ecting pitch change,diflerential pinions rotatably carried by said diflerential carrier inmesh with said diflerential gears, two power transmitting means, eachconnecting one control gear to one diii'erential gear, operative uponrotation of both said control gears in the same direction for rotatingsaid diil'erential gears in opposite directions when no pitch change isbeing eil'ected, whereby said differential carrier remains nonrotativewith respect to said craft when said control gears rotate as one withsaid hub. and means to rotate said differential carrier in one or theother direction with respect to said craft to provide relative rotationin one or the other direction between said control gears and said hub.

7. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitch change gear-set in said hub rotatable as a unit with said hub,said gear-set comprising an internally toothed reaction sear fast insaid hub and held against rotation with respect thereto, an internallytoothed driven gear within said hub secured to said blade root to bedriven therewith,

a planet pinion, a planet pinion carrier for said pinion rotatable insaid blade root and revolvably supporting said pinion in mesh with bothsaid ring gears, a sun gear rotatably supported in said carrier in meshwith said pinions, a bevel driving gear secured to said sun gear forunitary rotation therewith, two coaxial bevel control gears in mesh withthe first said bevel gear, adapted upon relative backward rotation ofone respect to the hub rotation, to rotate the driven gear for pitchincrease, and adapted upon relative backward rotation of the othercontrol gear with respect to hub rotation, to rotate the driven gear forpitch decrease, a differential gear-set comprising two differentialgears with coincident axes, a differential carrier normally nonrotativewith respect to said craft but rotatable about said coincident axes foreffecting pitch change, dlllerential pinions rotatably carried by saiddiil'erential carrier in mesh with said difierential gears, two powertransmitting means, each drivably connecting one control gear to onediil'erential gear, a. reversing gear included in one of said powertransmitting means, whereby, upon unitary rotation of both said controlgears in the same direction, said diilerential gears rotate at the samespeed in opposite directions when no pitch change is being effected,whereby said diilerential carrier remains nonrotative with respect tosaid craft when said control gears rotate as one with said hub, andmeans to rotate said diilerential carrier in one or the other directionwith respect to said craft to provide relative rotation in one or theother direction between said control gears and said hub.

8. In an adjustable pitch propeller for self-propeiled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitchchange gear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reaction gear fast in said huband held against rotation with respect thereto, an internally tootheddriven gear within said hub secured to said blade root to be driventherewith, a planet pinion, a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both said ring gears, a sun gear rotatably supported in saidcarrier in mesh with said pinions, a bevel driving gear secured to saidsun gear for unitary rotation therewith, two coaxial bevel control gearsin mesh with the first said bevel gear. adapted upon relative backwardrotation of one control gear with respect to the hub rotation, to rotatethe driven gear for pitch increase, and adapted upon relative backwardrotation of the other control gear with respect to hub rotation, torotate the driven gear for pitch decrease, means to retard said controlgears, one at a time, to produce relative backward rotation of the retarded control gear with respect to said hub rotation, a differentialgear-set comprising two difl'erential gears with coincident axes, adifferential carrier normally nonrotative with respect to said craft butrotatable about said coincident axes for effecting pitch change,differential pinions rotatably carried by said diilerential carrier in msh with said differential gears, two power transmitting means, eachdrivably connecting one control gear to one differential gear, areversing gear included in one of said power transmitting means,whereby. upon unitary rotation of both said control gears in the samedirection, said difierentlal gears rotate at the same speed in oppositedirections when no pitch change is being effected, whereby saiddifferential carrier remains nonrotative with respect to said craft whensaid control gears rotate as one with said hub, and means to rotate saiddifierential carrier in one or the other direction with respect to saidcraft to provide relative rotation in one or the other direction betweensaid control gears and said hub.

control gear with aavacss 9. In an adjustable pitch propeller icrselfpropelled craft, a hub, a blade having its root rotatable in saidhub about the blade axis, a pitch change gear-set in said hub rotatableas a unit with said hub, said gear-set comprising an internally toothedreaction gear fast in said hub and held against rotation with respectthereto, an internally toothed driven gear within said hub secured tosaid blade root to be driven therewith, a planet pinion, a planet pinioncarrier for said pinion rotatable in said blade root and revolvablysupporting said pinion in mesh with both said internally toothed gears,a sun gear rotatably supported in said carrier in mesh with saidpinions, at bevel driving gear secured to said sun gear for unitaryrotation therewith, a coaxial bevel control gear in mesh with the firstsaid bevel gear, adapted upon relative rotation of said control gear inone direction with respect to the hub rotation, to rotate the drivengear for pitch increase, and adapted upon relative rotation of thecontrol gear in the other direction with respect to hub rotation, torotate the driven gear for pitch decrease, a differential gear-setcomprising two diilerentiai gears with coincident axes, a difierentialcarrier normally nonrotative with respect to said craft but rotatableabout said coincident axes for effecting pitch change, diflerentialpinions rotatably carried by said differential carrier in mesh with saiddifferential gears, two power transmitting means, one of said powertransmitting means drivably connecting said control gear to onedifferential gear for unitary rotation, and the second of said powertransmitting means drivably connecting the propeller hub to the otherdiflerentiai gear, a reversing gear being included in one or said powertransmitting means, whereby, upon unitary rotation of said control gearand said hub in one direction, said differential gears rotate at thesame speed in opposite directions when no pitch change is beingefiected, whereby said differential carrier remains nonrotative withrespect to said craft whenever said control gear rotates as one withsaid hub. and means to rotate said differential carrier in one or theother direction with respect to said craft to provide relative rotationin one or the other direction between said control gear and said hub.

10. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitch change gear-set in said hub rotatable as a unit with said hub,said gear-set comprising an internally toothed reaction gear fast insaid hub and held against rotation with respect thereto, an internallytoothed driven gear within said hub secured to said blade root to bedriven therewith, a planet pinion, a planet pinion carrier for saidpinion rotatable in said blade root and revolvably supporting saidpinion in mesh with both said internally toothed gears, a sun gearrotatably supported in said carrier in mesh with said pinions, a beveldriving gear secured to said sun gear for unitary rotation therewith,two coaxial bevel control gears in mesh with the first said bevel gear,adapted upon relative backward rotation of one control gear with respectto the hub rotation, to rotate the driven gear for pitch increase, andadapted upon relative backward rotation of the other control gear withrespect to hub rotation, to rotate the driven gear for pitch decrease,means to retard said control gears, one at a time, to produce relativebackward rotation of the retarded control gear with respect to said hubrotation, a differential gear-set comprising two differential gears withcoincident axes, a differential carrier normally nonrotative withrespect to said craft but rotatable about said coincident axes foreffecting pitch change, differentlal plnions rotatably carried by saiddifferential carrier in mesh with said differential gears, two powertransmitting means, one of saidpower transmitting means drivablyconnecting one control gearto one differential gear for unitaryrotation, and the second of said power transmitting means drivablyconnecting the propeller hub to the other differential gear, a reversinggear being included in one of said power transmitting means, whereby,upon unitary rotation of said control gearaand'said hub in oqedirectionsaiddifferen'tial gears;r otate at these. ed ln'opposite dii ectlonswhenno pitch ehangeslagg I whereby said differential carrier rema nsnontotative with respect tosaid craft whenever said one control gearrotates'as one with said hub, and means to rotate said differentialcarrier in one or the other dlrection wlth' respect'to said i'dgggelative rotation in one or the between fsaidi control gears and l1'.In anadjustable pitch propeller for selfpropelled craft, a hub, a bladehaving its root rotatable in said hub about the blade axis, apitchchange gear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reactiongear fast in said huband held against rotation with respect thereto, an internally tootheddriven gear within said ifub secured to said blade root to be driventherewith, a planet pinion, a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both-'saidflnternally too'the'cYiZht-t a' sun gear rotataliilyr supporte'd -in isaidlcarrller in mesh with parser rotationofs'aid control, respect to the hub,rot ati on, to re gear for pitchincrease, and pasteaitip'gnireianve rotation of the control gear in"t'hecthe'rd'irectirin with respect to hub rotation l-o rp t-ptc the drivengear for pitch decrease; 'a' diiferentialgear-set' comprising twodifferential gears with' cpiricldent axes, a differential carrier"normally nonrot'it'ivc 'with respect to said craft but rotatable aboutsaid coincident axes for effecting pitch change. differential pinionsrotatably carried by said differential carrier in mesh with saiddifferential gears, two power transmitting means, one of said powertransmitting 'rneans drivably connecting said control gear to onedifferential gear for unitary rotation, and the second of said powertransmitting means drlvably connecting the propeller hub to the otherdifferential gear, a reversing gear being included in said second powertransmitting means. whereby, upon unitary rotation of said control gearand said hub In one direction, said differential gears rotate at thesame speed in opposite directions when no pitCh change is beingeffected, whereby said differential carrier remain: nonrotntlve withrespect to said craft Whenever said control gear rotates as one withsaid hub,

and means to rotate said diiierential carrier in iii) 12. In anadjustable pitch propeller for selfpropelled craft, a hub, a bladehaving its root rotatable in said hub about the blade axis, apitch-change gear-set in said hub rotatable as a unit with said hub,said gear-set comprising, an internally toothed reaction gear fast insaid hub and held against rotation with respect thereto, an internallytoothed driven gear within said hub secured to said blade root to bedriven therewith, a planet pinion, a planet pinion carrier for saidpinion rotatable in said blade root and revolvably supporting saidpinion in mesh with'both said internally toothed gears, a sun gearrotatably supported in said carrier in mesh with said pinlons, a beveldriving gear secured to said sun gear for unitary rotation therewith,two coaxial bevel control gears in mesh with the first said bevel gear,adapted upon relative-backward rotation "of'one control gear withrespect to the hub rotation, to rotate the driven gear for pitchincrease, and adapted upon relative backward rotation of the othercontrol gear with respect to hub rotation, to rotate the driven gear forpitch decrease, means to retard said control gears, one at a time, toproduce relative backward rotation of the retarded control gear withrespect to said hub rotation, a differential gear-set comprising twodlfierentlal gears with coincident axes, a differential carrier normallyrotative with respect to said craft but rotatable about said coincidentaxes for effecting pitch change, differential pin-' gears rotate atthe-same same speed in opposite directions when no pitch change is beingeffected,

whereby said dlfferentialcarrier remains nonrotative with respect tosaid craft whenever said one control gear rotates as one with said hub,and means to rotate said differential carrier in one or the otherdirection with respect to said to drain to provide relative rotation inone or the propelled craft, a hub, a blade having its root rotatable insaid hub about the bladeaxis, a pitch-change gear-set in said hubrotatable as a unit with said hub. said gear-set, comprising aninternally toothed reaction gear fast in said hub and held againstrotation with respect thereto, an internally toothed driven gearWithinsaid hub securedto said blade root to be driven therewith, aplanet pinion, a planet pinion carrier for said pinion rotatable in saidblade root and m d ably supporting said pinion in mesh with both saidinternally toothed gears, a sun gear rotat ably supported in saidcarrier in mesh with said pinions, a bevel driving gear secured to saidsun gear for unitary rotation therewith, a bevel control gear coaxialwith said hub,ln mesh with the first said bevel gear, adapted, uponrelative rotatlon of said control gear in one direction with respect tothe hub rotation, to rotate the driven gear for pitch increase, andadapted, upon relative rotation of the control gear in the otherdirection with respect to hub rotation, to rotate the driven gear torpitch decrease, a diiierential gear-set comprising two differentialgears with coincident axes, a, diflerential carrier normallynon-rotative with respect to said crait but rotatable about saidcoincident axes for efl'ecting pitch change, diflerential pinionsrotatably carried by said difierential carrier in mesh with saiddifierential gears, two power transmitting means, the first of saidpower transmitting means drivably connecting said control gear to onedifierential gear for unitary rotation, and the second or said powertransmitting means drivably connecting the propeller hub to the otherdifferential gear, a reversing gear being included in said first powertransmitting means, whereby, upon unitary rotation of said control gearand said hub in one direction, said difierential gears rotate at thesame speed in opposite directions when no pitch change is beingeiiected, whereby said differential carrier .remains nonrotative withrespect to said craft whenever said control gear rotates as one withsaid hub, and means to rotate said diflerentlal carrier in one or theother direction with respect to said craft to provide relative rotationin one or the other direction between said control gear and said hub.

14. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitch-change gear-set in said hub rotatable as a unit with said hub,said gear-set comprising, an internally toothed reaction gear fast insaid hub and held against rotation with respect thereto, an internallytoothed driven gear within said hub secured to said blade root to bedriven therewith, a planet pinion, a planet pinion carrier for saidpinion rotatable in said blade root and revolvably supporting saidpinion in mesh with both said internally toothed gears, a sun gearrotatabiy supported in said carrier in mesh with said pinions, a beveldriving gear secured to said sun gear for unitary rotation therewith,two coaxial bevel control gears in mesh with the first said bevel gear,adapted upon relative backward rotation 01' one control gear withrespect to the hub rotation, to rotate the driven gear for pitchincrease and adapted upon relative backward rotation a: the othercontrol gear with respect to hub rotation, to rotate the driven gear forpitch decrease, means to retard said control gears, one at a time, toproduce relative backward 'rotation or the retarded control gear withrespect to said hub rotation, a difl'erentlal gear-set comprising twodiiierential gears with coincident axes, a ditlerential carrier normallynonrotative with respect to said craft but rotatable about saidcoincident axes for effecting pitch change, difi'erential pinionsrotatably carried by said dilierential carrier in mesh. with saiddilierential gears, two power transmitting means, the first of saidpower transmitting means drivably connecting onecontrol gear to onedifferential gear for unitary rotation, and the second of said powertransmitting means drivably connecting the propeller hub to the otherdiflerential gear, a reversing gear being included in said first powertransmitting means, whereby, upon unitar rotation oi said control gearsand said hub in one direction, said differential gears rotate at thesame speed in opposite directions when no pitch change i being effected,whereby said differential carrier remains nonrotative with respect tosaid craft whenever said one control gear rotates as one with said hub,and means to rotate said diflerential carrier in one or the otherdirection with respect to said craft to provide relative rotation in oneor the other direction between said control gears and said hub.

15. In an adjustable pitch propeller for selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitch-change gear-set in said hub rotatable as a unit with said hub,said gear-set comprising an internally toothed reaction gear fast insaid hub and held against rotation with respect thereto,

internally toothed driven gear within said hub secured to said bladeroot to be driven therewith, a planet pinion, a planet pinion carrierfor said pinion rotatable in said blade root and revolvably supportingsaid pinion ln' mesh with both said internally toothed gears, a sun gearrotatably supported in said carrier in mesh with said pinions, a eveldriving gear secured to said sun gear for unitary rotation therewith, abevel control gear in mesh with the first said bevel gear, adapted uponrelative rotation of said control gear in one direction with respect tothe hub rotation, to rotate the driven gear for pitch increase, andadapted upon relative rotation of the said control gear in the otherdirection with respect to hub rotation, to rotate the driven gear forpitch decrease. a differential gear-set comprising two diilerentialgears with axis common with the control gear axis, the first 01 saiddifferential gears being drivably connected to said control gear, adirlerential carrier normally nonrotative with respect to said craft butrotatable about said common axis for effecting pitch change,differential pinions rotatably carried by said difierential carrier inmesh with both of said differential gears, a reversing gear train 0!which the first reversing gear and last reversing gear rotate inopposite directions, the first reversing gear being drivably connectedto the hub, and the last reversing gear being drlvably connected to thesec ond dillerential gear, and means to rotate said differential carrierin either direction with respect to said craft. 16. In an adjustablepitch propeller for selfpropelled craft, a hub, a. blade having its rootrotatable in said huh about the blade axis. a pltch-chanlle sear-set insaid hub rotatable as a unit with said hub, said gear-set comprising aninternally toothed reaction gear last in said hub and held againstrotation with respect thereto, an internally toothed driven gear withinsaid hub secured to said blade root to be driven therewith, a planetpinion, a planet pinion carrier for said pinion rotatable in said bladeroot and revolvably supporting said pinion in mesh with both saidinternally toothed gears, a sun gear rotatably supported in said carrierin mesh with said pinions, at bevel driving gear secured to said sungear for unitary rotation therewith, two coaxial bevel control gears inmesh with the first said bevel gear, adapted upon relative backwardrotation of one control gear with respect to the hub rotation, to rotatethe driven gear for pitch increase, and adapted upon relative backwardrotation of the other control gear with respect to hub rotation, torotate the driven gear for pitch decrease, means to retard said controlgears, one at a time, to produce relative backward rotation of theretarded control gear with respect to said hub rotation, a. diflerentialgear-set comprising two differential gears with axis common with thecontrol gear aids, the first or the two differential gears beingdrivabLy connected to one or said control gears, a differential carriernormally nonrotative with respect to said craft but rotatable about saidcommon axis for effecting pitch change, differential pinions rotatablycarried by said diflerential carrier in mesh with both of saiddiilerential gears, a reversing gear train of which the first reversinggear and last reversing gear rotate in opposite directions, the firstreversing gear being drivably connected to the hub, and the last beingdrivably connected to the second diflerentia. gear, and means to rotatesaid diflerential carrier in either direction with respect tosaid craft.

17. In an adjustable pitch propeller for a selfpropelled craft, a hub, ablade having its root rotatable in said hub about the blade axis, apitch-changegear-set in said hub rotatable as a unit with said hub, saidgear-set comprising an internally toothed reaction gear fast in said huband held against rotation with respect thereto, an internally tootheddriven gear within said hub secured to said blade root to be driventherewith, a planet pinion, a planet pinion carrier for said pinionrotatable in said blade root and revolvably supporting said pinion inmesh with both said internally toothed gears, a sun gear rotatablysupported in said carrier in mesh with said pinlens, a bevel drivinggear secured to said sun gear for unitary rotation therewith, two bevelcontrol gears, both coaxial with said hub, in mesh with the first saidbevel gear, adapted upon rotation,-the one in the same direction and theother opposite in direction to the hub rotation, to rotate the drivengear for pitch increase, and adapted, upon rotation, each opposite thefirst said directions to rotate the driven gear for pitch decrease, adiil'erential gear-set comprising two diil'erential gears with axescommon with the control gear axis, a differential pinion carriernormally nonrotative with respect to said craft but rotatable about saidcommon axis for eifectin pitch change, diiferential pinions rotatablcarried by said diflerential pinion carrier in mesh with saiddiflerential Sears, a reversing gear-set the first and last gears ofwhich rotate at equal speeds and in opposite directions when no pitchchange is being eflected and are respectively connected to one controlgear and one dlflerential gear, means connecting the other control gearto the other difl'erential gear for unitary rotation. and means torotate said diflerential carrier in either direction with respect tosaid craft.

18. In an adjustable pitch propeller, a hub, a blade having its rootrotatable in said hub about the blade axis, a pitch-change gear-set insaid hub rotatable as a unit with said hub, said gearset comprising aninternally toothed reaction gear fast in said hub and held againstrotation with respect thereto, an internally toothed driven gear withinsaid hub secured to said blade root to be driven therewith, a planetpinion, a planet pinion carrier for said pinion rotatable in said bladeroot and revolvably supporting said pinion in mesh with both saidinternally toothed gears, a sun gear rotatably supported in said carrierin mesh with said pinions, a bevel driving gear secured to said sun gearfor unitary rotation therewith, two bevel control gears, both coaxialwith said hub, in mesh with the first said bevel gear, adapted uponrotation, the one in the same direction and the other opposite indirection to the hub rotation. to rotate the driven gear for pitchincrease, and adapted, upon rotation, each opposite the first saiddirections to rotate the driven gear for pitch decrease, a differentialgear-set comprising two difl'erential gears with axes commen with thecontrol gear axis, a diii'erential pinion carrier rotatable about saidcommon axis, difl'erential pinion rotatably carried by said difierentialpinion carrier in mesh with said diflerential gears, a reversinggear-set, the first and last gears of which rotate at equal speeds andin opposite directions and are respectively connected to one controlgear and one diflerential gear, means connecting the other control gearto the other diflerential gear for unitary rotation, a brake elementattached to each diflerential gear for unitary rotation therewith.braking means for arresting rotation oi said elements one at a time, andmeans to rotate said diilerential carrier in either direction.

19. An adjustable pitch propeller comprising a hub, a blade having itsinner end rotatable in said hub about the axis or the blade, apitchchange gear-set in said hub rotatable as a unit with said hub,individual gears of said gear-set being rotatable relative to said hub,said gear-set including a driven gear on said inner end, two controlgears, and intermediate gears between the control gears and the drivengear, adapted, upon relative backward rotation 01' one control gear,with respect to the hub rotation, to rotate the driven gear for pitchincrease, and adapted, upon relative backward rotation of the othercontrol gear, with respect to hub rotation, to rotate the driven gearfor pitch decrease, electrically controlled braking means to retard saidcontrol gears, one at a time, to produce relative backward rotation orthe retarded control gear with respect to said hub rotation, adiflerential gear-set comprising two diil'erential gears with a commonaxis, a differential carrier rotatable about said common axis,diiierential pinions rotatably carried by said differential carrier inmesh with said differential gears, power transmitting means operative byrotation of said hub in one direction to rotate said dlflerential gearin opposite directions, at least one oi said diiferential gears beingdriven by one of said control gears, whereby said diiierential carrierremains nonrotative when said one control gear rotates as one with saidhub, a reversible electric motor to rotate said diflerentiai carrier inone or the other direction to provide relative rotation in one or theother direction between said control gears and said hub, speedreducingmechanism associated with said motor, including a low-speed shaft. alow-speed sear, clutch means drivably connecting said low-speed gear tosaid low-speed shaft, and electromagnetic means ior disengaging saidclutch, a current source, and a manual switch operable to one positionto series connect one or said electrically controlled braking mean andsaid electromagnetic means to said current source, and operable toanother position to series connect the other of said electricallycontrolled braking means and said electromagnetic means to said currentsource.

20. An adjustable pitch propeller comprising a hub, a blade having itsinner end rotatable in said hub about the axis or the blade, apitchchange gear-set in said hub rotatable as a unit with said hub,individual gears 01 said gear-set being rotatable relative to said hub,said gearset including a driven gear on said inner and, two controlgears, and intermediate gears between the control gears and the drivengear, adapted, upon relative backward rotation of one control gear, withrespect to the hub rotation, to rotate the driven gear for pitchincrease, and adapted, upon relative backward rotation of the othercontrol gear, with respect to hub rotation, to rotate the driven gearfor pitch decrease, electrically controlled braking means to retard saidcontrol gears, one at a time, to produce relative backward rotation ofthe retarded control gear with respect to said hub rotation, adiflerential gear-set comprisin: two diflerential gears with a commonaxis, a diflerential carrier rotatable about said common axis,diflerential pinions rotatably carried by said diflerential carrier inmesh with said diilerential sears, power transmitting means operative byrotation or said hub in one direction to rotate said differential searsin opposite directions. at least one or said diflerential gears beingdriven by one of said control gears, whereby said diiIerential carrierremains nonrotative when said one control gear rotates as one with saidhub, a reversibie electric motor to rotate said diflerential carrier inone or the other direction to provide relative rotation in one or theother direction between said control gears and said hub, speed reducinamechanism associated with said reversible motor, includins a low-speedshalt. a 1::-

one position one of said electrically controlled braking means, saidelectromaanetic means and said current source, and operable to anotherposition to provide a series circuit through the other of saidelectrically controlled braking means, said electromaenetic means 7, dsaid current source, a pitch-change-sensitive device drivable by saidlow speed s aft in one or the other direction upon pitch increase ordecrease, and pitch-chancelimiting switches, one in each said circuit,positioned in the path oi said pitch-change-sensitive device so as to beopened thereby at a predetermined pitch increase or decrease.

21. An adjustable pitch propeller comprising a hub, a blade havlnfl itsinner end rotatable in said hub about the axis or the blade, apitchchange gear-set in said hub rotatable as a unit with said hub,individual gears of said gear-set bein: rotatable relative to said hub,said gear-set including a driven gear on said inner end, two controlgears, and intermediate sears between the control gears and the drivengear, adapted, upon relative backward rotation or one control gear, withrespect to the hub rotation, to rotate the driven gear for pitchincrease, and adapted, upon relative baclrward rotation of the othercontrol gear, with respect to hub rotation, to rotate the driven gearfor pitch decrease. electrically controlled braking menu to retard saidcontrol gears, one at a time, to produce relative backward rotation ofthe retarded control gear with respect to said hub rotation, adiilerential gear-set comprising two diilerential gears with a commonaxis. a diflerential carrier rotatable about said common axis,diiierential pinions rotatably carried by said diiierential carrier inmesh with said diflerential sears. power transmitting means operative byrotation of said hub in one direction to rotate said diflerential gearsin opposite directions. at least one of said'diflerential gears beingdriven by one or said control gears, whereby said diiierential carrierremains nonrotative when said one control gear rotates as one with saidhub, is reversible electric motor havine two winding paths, adapted torotate said diflerential carriot in one or the other direction toprovide relative rotation in one or the other direction between saidcontrol gears and said hub, speed reducing mechanism associated withsaid reversible motor, a low-speed shaft, a low-speed gear,

connecting said low-speed gear to said low-speed shaft, and means fordis l sins said clutch, a current source, a manual switch operable toone position to provide a series circuit through one of saidelectrically controlled brakine means, said electromaenetie means, andsaid current source, and operable to another position to provide aseries circuit through the other 0! said electrically controlled brahngsaid electromaanetlo means and said current source, a speed-responsiveswitch operable to one position to provide a circuit through one windinspath and said current source, and operable to another position to rovidea circuit throush the g path and said current source, apitch-chandesensitive device, drivable by said low-speed shaftinoneortheotherdirectionuponpitchincrease or decrease, andpltch-chanae-llmiting switches, oneineachsaidcircuiapoaltipnedinthepathoi said pitch-chanse-sensitlve device so as to be opened thereby at apredetermined pitch increase or decrease.

22. An adjustable pitch propeller havin: a positive and a negative pitchranae, which comprises a hub, a blade having its inner end rotatable insaid hub about the axis of the blade. a pitch. change gear-set in saidhub rotatable as a unit with said hub, individual gears or said gear-sotbeinz rotatable relative to said hub, said gear-setmciudineadrivengearonsaidlnnerendtwo control gears. and in te gearsbetween control gear, rotate the driven gear for pitch decrease,electricallr controlled braking means to retard said control gears, oneat a time,

with respect to said hub rotation. a diiieren gear-set comps-lain: twodiileren gears with a common axis, a diiierential er rotatable throushone or said ing means. said electromagnetic means, and said currentsource, and operable to another position to provide a series circuitthrough the other of said electrically controlled braking means, saidelectrcmaanetic means and said current source,

